Surface Plasmon-coupled Fluorescence Research Articles

Mobile Phone Camera-Based Detection of Surface Plasmon-Coupled Fluorescence from Streptavidin Magnetic Nanoparticles and Graphene Oxide Hybrid Nanointerface

Surface plasmon-coupled fluorescence (SPCF) technique has developed as a highly sensitive, specific, and versatile methodology for quantitative and qualitative bioassays. It relies on the ability of prism-coupling approach to channelize the emitted photons into sharply directional emission with attributes of propagating surface plasmons resulting in highly p-polarized emission. There are voluminous research studies demonstrating the utility of wide range of nanomaterials as effective spacers in SPCF. Streptavidin magnetic nanoparticles (SMNPs) serve as excellent candidates for biomedical applications on account of their biocompatibility and tunable magnetic properties. From the perspective of magneto-plasmonics, although they are excellent candidates for SPCF explorations, they are underutilized in this domain. In this background, we report the first-time demonstration of quintessential integration of SMNPs and graphene oxide π-plasmons as crucial spacer material for augmented SPCF. The results obtained with exorbitant detector systems are substituted with reliable mobile phone camera based detectors, amenable for resource-limited settings.

Urine Cofilin-1 Detection for Predicting Type 1 Cardiorenal Syndrome in the Coronary Care Unit: A Gold Nanoparticle- and Laser-Based Approach

Background: Type 1 cardiorenal syndrome (CRS) is a severe complication for acute decompensated heart failure patients. This study aimed at evaluating the feasibility of using the gold nanoparticle-based localized surface plasmon-coupled fluorescence biosensor (LSPCFB) to detect urine cofilin-1 as a biomarker for predicting CRS among patients in the coronary care unit (CCU). Methods: A total of 44 patients were included with prospectively collected urine and blood samples. Both LSPCFB and conventional enzyme-linked immunosorbent assays (ELISAs) were used to measure urine cofilin-1 at admission to the CCU. The occurrence of CRS was judged within 7 days after admission. The discrimination presented as the area under the receiver operating characteristic curve (AUROC) and calibration of both detection methods were used to assess the predictive ability of urine cofilin-1 measured by the LSPCFB and ELISA. Results: Thirteen patients were diagnosed with CRS, while the other 31 patients were classified into a non-CRS group. For predicting CRS by measuring urine cofilin-1, the LSPCFB had higher accuracy (AUROC: 0.707, p = 0.031; overall accuracy: 79.55%) than the ELISA (AUROC: 0.479, p = 0.827; overall accuracy: 53.27%). The positive and negative predictive values of the LSPCFB were also higher than those of the ELISA (positive predictive value: 70.0 vs. 34.8%; negative predictive value: 82.4 vs. 76.2%). Conclusions: The gold nanoparticle-based immunoassay LSPCFB could exploit the potential of urine cofilin-1 as a single biomarker to predict CRS among CCU patients.

Silver–graphene oxide based plasmonic spacer for surface plasmon-coupled fluorescence emission enhancements

We report the application of single layered graphene oxide (SLGO) and silver decorated SLGO (Ag-SLGO) as plasmonic spacer material for obtaining enhanced fluorescence from a Rhodamine 6G (Rh6G) radiating dipole in a surface plasmon-coupled emission platform. To this end, we have decorated SLGO with biphasic silver nanoparticles using an in situ deposition technique to achieve 112-fold fluorescence enhancements.

Metal-Enhanced Fluorescence: Wavelength-Dependent Ultrafast Energy Transfer

The fluorescence of dye molecules often shows a strong increase in intensity near metal surfaces or nanoparticles. The excited-state dynamics of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) in the presence of a silver island film (SIF) were explored by femtosecond transient absorption spectroscopy. Under 403 nm excitation, we found clear differences in the excited-state spectra and kinetics of DCM with the SIF. From the analysis of the emission kinetics of DCM, an additional process with a 40–60 ps time constant was distinguished, which was hypothesized to be surface plasmon-coupled fluorescence. This ultrafast process for 403 nm excitation was confirmed as ultrafast energy transfer directly from the surface plasmon of the SIF to DCM. Under 480 nm excitation, no such ultrafast process was observed, but a constant increase in the emission intensity by ∼10% due to the increased electric field of the silver nanoparticles occurred.

Plasmonic amplification for bioassays with epi-fluorescence readout.

Corrugated metallic surfaces offer means for efficient amplification of fluorescence bioassay signal based on the near field coupling between surface plasmons and fluorophore emitters that are used as labels. This paper discusses the design of such plasmonic structure to enhance the sensitivity of immunoassays with epi-fluorescence readout geometry. In particular, crossed gold grating is theoretically and experimentally investigated for combined increasing of the excitation rate at the fluorophore excitation wavelength and utilizing directional surface plasmon-coupled fluorescence emission. For Alexa Fluor 647 dye, the enhancement factor of around EF = 102 was simulated and experimentally measured. When applied to a sandwich interleukin-6 immunoassay, highly surface-selective enhancement reaching a similar value was observed. Besides increasing the measured fluorescence signal associated with the molecular binding events on a surface by two orders of magnitude, the presented approach enables measuring kinetics of the surface reaction that is otherwise masked by strong background signal originating from bulk solution.

Biomarker Analysis with Grating Coupled Surface Plasmon Coupled Fluorescence

One of the greatest hurdles in protein microarray technology has been the limited sensitivity. However, the strategy of amplifying the SPR signal with fluorescence improves sensitivity. Herein, we report a simple and efficient method, Grating Coupled Surface Plasmon Coupled Fluorescence (GCSPCF) with a peptide microarray to screen sera of human subjects and a mouse strain with autistic-like behavior for quantification of the epitope specificities of their circulating antibodies. The GCSPCF peptide microarray is a novel assay that facilitates high-throughput screening of antibody epitope specificities or binding of interacting analytes with a small quantity (<50 μl) of sample. This study utilized over 600 peptides with the eventual goal of being able to identify antibodies that could be used as biomarkers of particular disorders. The GCSPCF technology was able to detect antibodies to the tripeptide glutathione; it was also capable of sequential screening antibodies of different immunoglobulin isotypes (IgG1, IgG4 and IgE) to the same peptide. The GCSPCF broad-based screening approach was able to begin the identification of Original Research Article Mendoza et al.; JABB, Article no. JABB.2014.001 2 epitope-specific antibody binding patterns in an effort to develop a predictive signature that could be further developed for clinical trials. In addition to evaluation of antibody specificities with hundreds of spotted peptides at multiple regions of interest (ROI), the addition of spotted antibodies could provide an even more complete biomarker profile with capture of analytes, such as stress proteins and cytokines. Differences between a mouse strain with normal behaviors (C57BL/6J) and a strain with autistic-like behaviors (BTBR T + tf/J) as well as healthy and autistic participants are used for comparative analyses.

Determination of urine cofilin-1 level in acute kidney injury using a high-throughput localized surface plasmon-coupled fluorescence biosensor

The actin-depolymerizing factor (ADF)/cofilin protein family has been reported to be associated with ischemia-induced renal disorders. We examine whether cofilin-1 is associated with acute kidney injury (AKI) using human urine samples. We exploited a 96-well based high-throughput biosensor that uses gold nanoparticles and a sandwich immunoassay to detect the urine cofilin-1 level of AKI patients. The mean urine cofilin-1 level of the AKI patients (n=37 from 47 cases analyzed) was twofold higher than that of healthy adults (n=21 from 29 cases analyzed). The receiver operating characteristic (ROC) curve showed that cofilin-1 was acceptable for discriminating AKI patients from healthy adults. However, an increase of the sample size is required to conclude the importance of urine cofilin-1 on AKI diagnosis, and the high-throughput ultrasensitive biosensor used in this study would greatly accelerate the measurement of urine cofilin-1 in an increased sample size.

Detection of urine cofilin-1 from patients hospitalized in the intensive care unit using the metal-enhanced fluorescence technique

Abstract Ischemic shock and acute kidney injury (AKI) are the primary causes of high mortality in the intensive care unit (ICU) patients. In a rat model, ischemia is able to disrupt the actin cytoskeleton of proximal tubule cells. This effect is associated with the expression and excretion of actin depolymerizing factor (ADF)/cofilin. However, the human evidence of ADF/cofilin excreted in ICU patients with ischemic shock and/or AKI remains to be addressed. Here we developed a 96-well high-throughput, localized surface plasmon-coupled fluorescence biosensor (HT-LSPCFB) combining a sandwich immunoassay to measure the urine cofilin-1 in 57 ICU patients and 8 healthy controls. A linear relationship between 1 and 10 5 pg/mL of human cofilin-1 recombinant protein was determined ( R 2 = 0.9845) in this study. The highest normalized cofilin-1 levels obtained in the ICU patients and healthy adults were 1.985 and 0.726, respectively. The mean normalized cofilin-1 level of total ICU patients (0.7403) was also significantly higher than that of healthy adults (0.4759) ( p = 0.0052). An examination of the receiver operating characteristic (ROC) curve and area under curve (AUC) showed that cofilin-1 is acceptable for assessing the ICU patients (AUC = 0.775) and shock (AUC = 0.713), but not for AKI (AUC = 0.681). Therefore, the HT-LSPCFB is suitable for detecting the urine cofilin-1 which potentially becomes a prognostic factor for ICU patients with shock.

UV to NIR Surface Plasmon Coupled and Metal-Enhanced Fluorescence Using Indium Thin Films: Application to Intrinsic (Label-less) Protein Fluorescence Detection

Surface plasmon coupled fluorescence (SPCF) and metal enhanced fluorescence (MEF) over a broad wavelength range from UV to NIR are demonstrated from 20 nm thin indium films. Steady-state and time-resolved fluorescence measurements of fluorophores deposited on the indium thin films indicate enhancement of the fluorescence intensity along with decreases in decay times, both in MEF and SPCF modes, accompanied by an increase in photostability. MEF was found to be more pronounced for the red emission dye with respect to a blue emission dye. A completely p-polarized directional emission for three fluorophores from a hemicylindrical prism at 44° indicates surface plasmons couple with the near field dipoles at the interface of the indium-sample. The evanescent waves generated at the interface are calculated to penetrate more deeply for longer wavelength excitation with respect to shorter wavelengths, and the penetration depth nearly doubles in comparison to that of the widely used silver thin films. As an applica...

Long range surface plasmon-coupled fluorescence emission for biosensor applications

A biosensor scheme that employs long range surface plasmons (LRSPs) for the efficient excitation and collection of fluorescence light from fluorophore-labeled biomolecules captured in a three-dimensional hydrogel matrix is discussed. This new approach to plasmon-enhanced fluorescence (PEF) is experimentally and theoretically investigated by using the Kretschmann configuration of attenuated total reflection (ATR) method. A layer structure supporting LRSPs that consists of a low refractive index fluoropolymer layer, a thin gold film and a large binding capacity N-isopropylacrylamide (NIPAAm)-based hydrogel matrix swollen in an aqueous sample is employed. By using this layer architecture, the extended field of LRSPs probes the binding of biomolecules in the binding matrix at up to micrometer distances from the gold surface. With respect to regular surface plasmon-enhanced fluorescence spectroscopy (SPFS) and surface plasmon-coupled emission (SPCE), a narrower angular distribution of the fluorescence light intensity, a larger peak intensity and the excitation and emission at lower angles were observed.

Directional, Broad, and Fixed Angle Surface Plasmon Coupled Fluorescence from Iron Thin Films

Fixed angle surface plasmon coupled fluorescence (SPCF) from iron thin films is demonstrated for the first time. The optimum thickness of the iron thin films was determined to be 15 nm using Fresnel calculations. The angles of minimum reflectivity for light at 496-814 nm were predicted to occur at a fixed and broad range of angles of 60-70°. Experimental corroboration of these predictions were undertaken by employing fluorescein isothiocyanate (emission peak at 517 nm), rhodamine B (580 nm), zinc phthalocyanine (710 nm), and IR 780 dye (814 nm). SPCF emission from all four fluorophores was directional, p-polarized, and observed at a fixed angle of ∼65°.

Image Formation in Wide-Field Microscopes Based on Leakage of Surface Plasmon-Coupled Fluorescence

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A proof-of-concept imaging technique that combines the advantages of wide-field surface plasmon, leakage radiation, and total internal reflection fluorescence microscopy methods is presented. High-contrast non-scanning images with subwavelength resolution of patterned and homogeneous samples coated with a fluorescent material were demonstrated. We show that the image formed in the back focal plane of the objective lens can be reconstructed from the image of the sample's surface using an algorithm similar to that used in computerized tomographic imaging. Our experimental results suggest that there is a 1-D Fourier transform relationship between any line amplitude profile at a given angle passing through the center of the sample's surface image and a line amplitude profile passing through the center of the back-focal-plane image at the same angle. </para>

Surface Plasmon Coupled Fluorescence in the Visible to Near-Infrared Spectral Regions using Thin Nickel Films: Application to Whole Blood Assays

Nickel thin films thermally evaporated onto glass supports are used to demonstrate surface plasmon coupled fluorescence (SPCF) over a broad 400 nm wavelength range (400-800 nm) for potential assays that can be run in buffer and/or whole blood. In contrast to traditional fluorescence-based assays, SPCF converts otherwise isotropic emission into highly directional and polarized emission, an attractive concept for surface assays. Theoretical Fresnel calculations performed in the ultraviolet to near-infrared spectral range (344-1240 nm) predict the near-field generation of surface plasmons in 15 and 20 nm nickel thin films. The angles of minimum reflectivity for nickel thin films with 10 nm SiO(x) and 30 nm polymer overcoats over the 428-827 nm wavelength range occur over a 10 degree range. To experimentally corroborate the theoretical calculations, a polymeric solution of five different fluorophores, POPOP (lambda(max, emission) = 428 nm), FITC (517 nm), S101 (600 nm), Zn PhCy (710 nm), and IR 780 (814 nm), were spin coated separately onto 15 and 20 nm nickel thin films. SPCF intensity (s- and p-polarized) from fluorophores at the corresponding emission lambda(max) was measured at angles between 0-90 degrees. In addition, the free-space emission and SPCF intensity of FITC on 20 nm nickel thin film were also measured to demonstrate the angular-dependent nature of SPCF. SPCF from nickel thin films was p-polarized and highly directional with lambda(max) confirmed at an angle of 65 degrees for all the fluorophores as predicted by Fresnel calculations. The utility of nickel thin films for whole blood bioassays is demonstrated with a long-wavelength fluorophore, where the SPCF intensity of Zn PhCy (50 pM-50 microM) in whole blood at 710 nm was measured at 65 degrees. Using Fresnel calculations it is also predicted that the evanescent field above the nickel films penetrates deeper into solution than for other metals used to date for SPCF, an attractive notion in SPCF-based biosensing applications.

Silver island nanodeposits to enhance surface plasmon coupled fluorescence from copper thin films

A method to enhance surface plasmon coupled fluorescence (SPCF) from thin copper films using silver islands as an overlayer is presented. Silver islands were deposited onto copper thin films using a wet chemical technique for up to 60 s, which resulted in surface features ranging from randomly sized silver nanoparticles to a silver thin film. Theoretical Fresnel calculations predict the coupling of light to copper thin films with a silver overlayer. SPCF and the free-space emission intensities from Rhodamine B spin-coated onto silvered copper were found to be significantly larger than measured from the copper thin films alone.

Surface Plasmon Coupled Fluorescence in the Ultraviolet and Visible Spectral Regions Using Zinc Thin Films

The use of zinc thin films deposited onto glass supports for surface plasmon coupled fluorescence (SPCF) over a broad 200 nm wavelength range is demonstrated. Fresnel calculations performed in the ultraviolet and visible spectral range are predicted to generate surface plasmon modes in 30 nm zinc thin films. In this spectral range, the extent of coupling of light to zinc thin films was shown to be significant as compared to similar aluminum, gold, and silver thin films. The experimental demonstration of SPCF using 30 nm zinc thin films in the ultraviolet and visible spectral regions was undertaken using three different fluorophores 2-AP, POPOP, and FITC, respectively. Surface plasmon coupled fluorescence from zinc thin films was p-polarized and highly directional with lambda max conferred at an angle of 58, 68, and 60 degrees for FITC, POPOP, and 2-AP, respectively. s-Polarized emission from zinc thin films was negligible for all fluorophores except for a sample spin coated from a 10% PVA solution, which resulted in significant s-polarized emission due to the generation of waveguide modes. The experimental results are consistent with reflectivity curves that are theoretically predicted using Fresnel calculations. Given the growing use and utility of plasmon-enhanced fluorescence in the analytical and biological sciences, our findings will serve as a useful tool for workers in the ultraviolet and visible spectral regions.

Surface plasmon coupled fluorescence from copper substrates

Previously, we reported the observation of metal enhanced emission from copper nanoparticles. In this letter, we report the observation of surface plasmon coupled fluorescence (SPCF) or emission from thin copper (Cu) continuous films. Using Fresnel calculations to theoretically calculate the reflectance curves for polymethyl methacrylate films doped with sulforhodamine 101, we correlated the minimum reflectance angles for both s- and p-polarized lights with maximum fluorescence emission. These observations reveal that we can achieve SPCF with copper substrates and possibly design inexpensive copper substrates for fluorescent sensing applications and potentially, fluorescent based electrical signals and circuits.

Microwave-Triggered Surface Plasmon Coupled Chemiluminescence

We describe a high sensitivity and rapid sensing technology for the detection and determination of surface-bound proteins/enzymes and potentially even DNA/RNA. Low power microwave pulses are used to “trigger” chemiluminescence “on demand” at the tips of planar triangular structures. When the triangles are deposited on 40 nm thick continuous silver films with a spacer layer, the intense pulsed chemiluminescence photon bursts become highly polarized and directional through the back of the film, as compared to traditional weak free-space isotropic emissions. Subsequently, microwave-triggered surface plasmon coupled chemiluminescence (MT-SPCC) appears to be a significant improvement over traditional chemiluminescence “slow glow” for surface assays, as well as other surface plasmon coupled fluorescence based assay technologies, such as surface plasmon coupled emission (SPCE) and surface plasmon coupled fluorescence (SPCF). Mw − Microwave pulses to locally “trigger” chemiluminescence, No Mw − No Microwave pulses, i.e. traditional chemiluminescence “slow glow”.

Red blood cells do not attenuate the SPCE fluorescence in surface assays

We describe the positive effect of surface plasmon-coupled fluorescence emission (SPCE) on the detection of a signal from a surface immunoassay in highly absorbing or/and scattering samples. A model immunoassay using fluorescently labeled anti-rabbit antibodies that bind to rabbit immunoglobulin on a silver surface was performed, and the signal was detected in the presence of various highly absorbing and/or scattering solutions or suspensions, such as hemoglobin solution, plastic beads, and red blood cells. The results showed that a highly absorbing solution consisting of small molecules (dye, hemoglobin) attenuates the SPCE signal approximately 2-3-fold. In contrast, suspensions with the same absorption containing large particles (large beads, red blood cell suspension) attenuate the SPCE signal only slightly, approximately 5-10%. Also, a suspension of large undyed, highly scattering beads does not reduce the SPCE signal. The effects on the immunoassay signal of the sample background absorption and scattering, the size of the background particles, and the geometry of the experimental set-up are discussed. We believe that SPCE is a promising technique in the development of biosensors utilized for surface-based assays, as well as any assays performed directly in highly absorbing and/or scattering solutions without washing or separation procedures. Figure Red blood cells (unlike hemoglobin) do not attenuate the SPCE fluorescence in surface assays.

Localized Surface Plasmon Coupled Fluorescence Fiber-Optic Biosensor with Gold Nanoparticles

A novel fiber-optic biosensor based on a localized surface plasmon coupled fluorescence (LSPCF) system is proposed and developed. This biosensor consists of a biomolecular complex in a sandwich format of <antibody/antigen/Cy5-antibody-gold nanoparticle (GNP)>. It is immobilized on the surface of an optical fiber where a <Cy5-antibody-GNP> complex forms the fluorescence probe and is produced by mixing Cy5-labeled antibody and protein A conjugated gold nanoparticles (Au-PA). The LSPCF is excited by localized surface plasmon on the GNP surface where the evanescent field is applied near the core surface of the optical fiber. At the same time, the fluorescence signal is detected by a photomultiplier tube located beside the unclad optical fiber with high collection efficiency. Experimentally, this novel LSPCF biosensor is able to detect mouse immunoglobulin G (IgG) at a minimum concentration of 1 pg/mL (7 fM) during the biomolecular interaction of the IgG with anti-mouse IgG. The analysis is expanded by a discussion of the amplification of the LSPCF intensity by GNP coupling, and overall, this LSPCF biosensor is confirmed experimentally as a biosensor with very high sensitivity.